1. Field of the Invention
This invention is concerned with aliphatic diisocyanates useful as polyurethanes. The present invention is also concerned with the process for preparing said diisocyanates.
2. Description of the Prior Art
A wide variety of both aliphatic and aromatic di- and higher polyisocyanates have been disclosed, as well as diverse methods of their preparation. In many instances such isocyanates are difficult and/or uneconomical to prepare. In yet other cases the amine precursors to the isocyanates have to be prepared in steps involving acid neutralization and removal of subsequent salt formation. For example, polymeric polyisocyanates are prepared by first preparing the polyamines via a reaction involving neutralization with base followed by salt removal. More specifically, aniline is reacted with formaldehyde in the presence of a strong mineral acid such as hydrochloric acid to provide a reaction mixture which upon neutralization with a base may be treated to recover polyphenylamines. It is necessary to utilize large quantities of both a mineral acid and base which adversely affect the economics of the process and also the ease in conducting the reaction. In addition, use of large quantities of mineral acids and bases presents a severe corrosion problem.
It therefore would be an advance in the art to provide a new class of diisocyanates prepared directly from a diamine whose preparation does not involve the just-mentioned drawbacks.